In recent years, there have been developed seven-axis articulated robots which have one more axis (redundant axis) than used in conventionally, widely-used six-axis articulated robots. In seven-axis articulated robots, the pivot angle of the pivot axis of each joint is obtained from the position and posture of a wrist by inverse transform operation similarly to the case of six-axis articulated robots. However, in the seven-axis articulated robots, the pivot position of each axis is not determined uniquely by specifying the position and posture of the wrist, although in the six-axis articulated robots, the pivot position of each axis is uniquely determined by specifying the position and posture of the wrist. The reason for this is that the presence of the redundant axis allows the elbow portion to change its position with a hand end kept at a position. Therefore, in the seven-axis articulated robots, it is necessary to teach not only the position and posture of the wrist but also the position and posture of the whole of the articulated robot, when taking account of influences upon obstacles surrounding the robot.
There are known methods for controlling a seven-axis articulated robot. In one method, control is performed with the redundant axis being fixed (see e.g., Patent Literature 1). Another control method is such that control is performed with the angle of the elbow portion kept constant. There is also known a teaching method for a seven-axis articulated robot in which an operating zone of a robot arm is divided into a plurality of regions and a reference position and a reference posture for the robot arm for every divided region are taught beforehand (see e.g., Patent Literature 2).